Technical Abstract:
Shiga toxin-producing E. coli (STEC) comprise a serologically diverse group of organisms that have caused disease in humans and animals. In 2000, the USDA's National Animal Health Monitoring System (NAHMS) conducted a study carried out by the Animal and Plant Health Inspection Service with the collaboration of the Agricultural Research Service to determine the prevalence and characteristics of STEC harbored by swine in the U.S. Fecal samples collected from swine operations from 13 of the top 17 swine-producing states from September 2000 to March 2001 were tested for the presence of STEC. Ten grams of fecal samples were subjected to enrichment in tryptic soy broth then, following DNA extraction, the samples were tested for the presence of stx1 and stx2 using the TaqMan® E. coli STX1 and STX2 PCR-based assay. Enrichments of samples positive for stx1 and/or stx2, were plated onto Luria Bertani agar, and colony hybridization was performed using digoxigenin-labeled probes for stx1 and stx2. Colonies corresponding to spots on the membranes were picked and confirmed by the PCR for the presence of the stx1, stx2, or stx2e genes, and the isolates were serotyped. Out of 687 total fecal samples tested, 54%, 64%, and 38% were positive for stx1, stx2, or for both toxin genes, respectively, using the TaqMan® E. coli STX1 and STX2 Kit. Out of 328 isolates, 54 produced stx1, 14 produced stx2, and 260 produced stx2e. Four fecal samples had isolates that possessed stx1 and isolates that possessed either stx2 or stx2e. The STEC isolates belonged to various serogroups including O2, O8, O15, OX18, O20, O57, O65, O68, O78, O91, O101, O120, O121, O152, O158, O159, O160, O163, and O untypable. Results of this study indicate that swine in the U.S. harbor STEC that may potentially cause human illness.